There are many industries interested in providing items that are free from bacteria, viruses, fungi, spores, and other pathogenic microorganisms, including the food industry, the medical industry, waste management industry, and many others. For example, hospitals, doctor offices, dentist offices, veterinary offices and other providers of medical services to humans or animals require sterile items, such as medical instruments, surgical linens, etc., free from pathogenic microorganisms.
Although there are several approaches for sterilizing items, including heat sterilization, chemical sterilization, radiation, etc., heat sterilization is the most common approach to providing sterile items. Several heat sterilization procedures are currently in practice and include both wet and dry sterilization. Wet heat sterilization is considered the most dependable procedure for the destruction of microorganisms and typically includes water (steam) as the working fluid for achieving sterilization. Dry sterilization, on the other hand, uses a dry gas as its working fluid, is less efficient, and typically requires higher temperatures and longer exposure times to achieve sterile conditions. For example, steam sterilization uses pressurized steam at 121° C.-134° C. for about thirty to forty minutes while dry sterilization typically requires a temperature of between 160° C.-170° C. for an exposure time of between two to four hours. Accordingly, the various industries, including the medical industry, focus primarily on wet sterilization procedures.
Conventionally, in hospitals, doctor offices, etc., the commonly employed procedure for wet sterilization is autoclaving. In autoclaving, the item(s) to be sterilized, such as, for example, bandages, operating gowns and other linens, surgical knives, forcipes, and other instruments, are positioned within a chamber of an autoclave. Saturated steam generated by, typically, an external steam generator (e.g., boiler) is introduced into the chamber and has a temperature of approximately 100° C. Because it is difficult to kill microorganisms at this temperature in a relatively short period of time, the pressure in the chamber may be increased so as to raise the temperature of the steam. For example, for saturated steam to have a temperature of approximately 121° C., the chamber must be pressurized to approximately 30 psi. The pressure required to reach higher temperatures correspondingly increases. For example, for the steam to have a temperature of approximately 134° C., the chamber must be pressurized to approximately 44 psi. Once the operational temperature/pressures has been reached, the conditions are maintained within the chamber for a prescribed period of time to achieve sterilization of the items. After the sterilization period, the pressure in the chamber is released so as to allow removal of the sterilized items. Use of an autoclave, while being primarily associated with the destruction of microorganisms, may be used in other applications as well. For example, autoclaves may be used in various metallurgy processes, ceramic processes, etc.
While autoclaving has been generally successful for its intended purpose of sterilizing various items, including items for the medical industry, there are some drawbacks to this practice. For example, autoclaves effectively operate as pressure vessels and thus their design and use may be regulated by various local, state and/or federal regulations or standards for ensuring proper and safe operation thereof. Meeting the standards often results in the autoclave having a relatively heavy, bulky design with increased overall costs. Additionally, autoclaves typically require relatively large steam generators. In this regard, because the autoclave operates at increased pressures, a significant amount of steam has to be generated to reach saturated conditions inside the chamber at the elevated temperatures. The amount of steam required at the increased pressures mandates that relatively large steam generators be utilized. For relatively small autoclaves (e.g., small office use), the steam generators may be built into the autoclave or located immediately adjacent to the autoclave. Such autoclaves having the steam generator therewith tend to be heavy and bulky. In addition, the relatively large steam generators increase the table, floor, or countertop space (i.e., machine footprint) occupied by the autoclave.
For relatively large autoclaves, the steam generator may not be positioned locally (i.e., integrated into the autoclave or immediately adjacent the autoclave), but instead may be remotely located. For example, hospitals, universities, and other large building, campuses, etc. may have a centralized boiler that provides steam to many locations throughout the larger structure or community. In this regard, piping or other conduits carry the steam from the boiler throughout the larger structure. Because the steam is transported over appreciable distances, such systems are susceptible to heat loss, which affects the quality of the steam; leaks, which result in a loss of pressure, mass flow, etc. and require frequent and costly maintenance; and other factors which diminish the effectiveness of such remotely located steam generators. Furthermore, dedicated ports for accessing the steam lines are predetermined (e.g., during construction of the building, campus, etc.) so that the location of the autoclave within a hospital room, laboratory, etc. is limited. This in turn limits the design considerations for the space in which the autoclave is to be located. Attempts to relocate a steam port are difficult and costly and are thus generally discouraged by maintenance personnel and the like.
In addition to the above, autoclaves lack the robustness of sterilizing devices required by current applications and also lack the robustness to meet the future challenges of providing sterilized items free from microorganisms. For example, autoclaves typically utilize only one type or mode of sterilization, i.e., wet heat sterilization, and typically operate using only a single working fluid, i.e., water. However, there are instances when other sterilization techniques may be desired. For example, it may be desired to use dry heat sterilization to kill certain microorganisms or with certain items suitable for dry heat sterilization. In such cases, the autoclave is incapable of operating in a dry heat sterilization mode and a completely separate device is typically required. Having two separate devices increases costs and may utilize valuable table, floor, or countertop space. Additionally, operators must be appropriately trained to operate multiple, perhaps significantly different devices. Such situations may result in increased operator error.
Furthermore, in some applications, it may be desirable to augment wet heat sterilization with other types of sterilization. For example, in some applications it may be desirable to use radiation, including ultraviolet (UV) radiation, infra red (IR) radiation, x-rays, microwaves, and other forms of radiation, in combination with wet heat sterilization processes. Moreover, in other applications, it may be desirable to use a form of chemical sterilization in combination with a wet heat sterilization process. With autoclaves, however, incorporating such additional or auxiliary sterilization is problematic due to the need to pressurize the chamber. Thus, any additional sterilization using one of these other processes requires a separate device and separate processing steps to achieve such additional sterilization.
Perhaps a more serious flaw of autoclaves, however, is that autoclaves are incapable of operating over a selected temperature range. Instead, autoclaves are typically designed to operate at a predetermined temperature. More particularly, autoclaves typically operate at either 121° C. or 134° C. depending on the particular sterilization application. Unfortunately, many in the scientific community anticipate that in the future, higher temperatures will be required to kill certain microorganisms. For example, sterilization procedures at approximately 140° C., 180° C., or even higher may be required to kill resistant bacteria, viruses, and other pathogenic microorganisms. For higher wet heat temperatures, the corresponding pressure in the autoclave must significantly increase. Current autoclaves, however, are not readily modifiable so as to operate at these elevated temperatures. More particularly, to get to these elevated temperatures, the chamber of the autoclave will have to be pressurized to approximately 52 psi, 145 psi, respectively, or higher. Current autoclaves simply are not designed to operate at these elevated pressures. Accordingly, current autoclaves will have to be summarily replaced with new, larger, and heavier autoclaves rated for the elevated pressures and temperatures. Such wholesale replacement would be cost prohibitive to many facilities for which sterilization is essential. In addition to the above, autoclaves may pose a health hazard, as more fully discussed at www2.umdnj.edu/eohssweb/aiha/accidents/autoclave.htm, the disclosure of which is incorporated by reference herein in its entirety.
The use of superheated steam at atmospheric pressures has been proposed in other, non-medical industrial applications. By way of example, U.S. Pat. No. 6,161,306 is directed to apparatus and methods of drying a load of moist fibrous material (e.g., a load of laundry) using superheated steam at atmospheric pressures. The '306 patent, however, is devoid of any disclosure or appreciation of aspects relating to antimicrobial effects. It is believed that the apparatus disclosed in the '306 patent is incapable of generating a high percentage of steam within the enclosure. As discussed below, however, for antimicrobial applications similar to that for which autoclaves are typically used, high concentrations of steam may be required.
U.S. Pat. No. 7,113,695 is directed to heat treating various items, such as various odoriferous food items, wherein superheated steam and a dry distillation gas is recirculated through a chamber holding the items and the steam and dry distillation gas are channeled through a deordorizer filter to deodorize the steam and gas. It is believed that due to the presence of the dry distillation gas, the apparatus would be incapable of achieving a high concentration of steam within the chamber.
U.S. Pat. No. 5,711,086 is directed to an open system for continuously drying moist materials. It is also believed that the apparatus described in the '086 patent will be incapable of achieving a high concentration of steam within its chamber. U.S. Pat. No. 6,900,421 is directed to a sterilizing apparatus using microwave heating for generating superheated steam. U.S. Pat. No. 6,880,491 is directed to generating superheated steam using hydrogen peroxide and a combustible fluid, wherein the combustion process decomposes the hydrogen peroxide to produce superheated steam. U.S. Pat. No. 7,115,845 is directed to a superheated steam generator that uses electromagnetic induction to produce the superheated steam. U.S. Pat. No. 7,079,759 is directed to a device for generating saturated steam not superheated steam.
Accordingly, there is a need for an improved sterilizing apparatus and method for sterilizing items that overcomes these and other drawbacks of current autoclaves and prior art systems. More particularly, there is a need for a sterilizing apparatus and associated method that can operate at atmospheric pressure; that include localized steam generators that are smaller and lighter than conventional steam generators; that are versatile; that are capable of operating over a relatively large temperature range; that are capable of producing a high concentration of steam within the chamber; that are capable of operating in different modes or in combination with a host of other sterilization procedures; and that are capable of heating and concentrating the fluid continuously or intermittently independent of any pressure increase or decrease in the chamber.